The present invention relates to communications networks. More particularly, and not by way of limitation, the present invention is directed to a system and method for media gateway negotiation in a telecommunications network.
A layered network architecture is commonly used in telecommunication networks. At call setup, a Call Control Node (CCN) acts as a Media Gateway Controller (MGC). The CCN, such as a Mobile service Switching Center (MSC), Gateway MSC (GMSC), a Transit Switching Center (TSC) or a Media Gateway Control Function (MGCF), selects a Media Gateway (MG) to switch the user plane and to provide in-band equipment if necessary.
In many call cases, multiple CCNs are involved in call setup. Call setup information is signaled between CCNs using call control protocols, such as Integrated Services Digital Network User Part (ISUP), Bearer Independent Call Control (BICC) or Session Initiated Protocol (SIP). When a CCN selects a MG, call control protocols may provide a capability to send the identifier of the selected MG to the succeeding CCN. The succeeding CCN has the choice to select the same MG for user plane switching. In many cases selecting the same MG in subsequent CCN's allows better resource utilization in the nodes and in the network.
One typical call setup scenario for telephone calls (mobile or fixed), utilizes a procedure of forward bearer setup. In this scenario, the bearer is established from the calling side towards the called side. FIG. 1 is a simplified block diagram of forward bearer setup utilizing the BICC call control protocol. A preceding CCN 10 and a succeeding CCN 12 each controls a MG (MG 14 and MG 16 respectively) for user plane switching. In order to achieve forward bearer setup, the succeeding CCN 12 selects a MG first and sends a MG identifier and bearer address information backwards to the preceding CCN 10. The preceding CCN 10 then selects the MG and initiates bearer setup procedure. A mobile station (MS) 20 may operate in, for example, a GSM/EDGE Radio Access Network (GERAN) 22. The CCN 10 communicates with the mobile station 20. An MS 24 operates in a GERAN 26 and communicates with the CCN 12. The CCN 10, CCN 12, MS 20, and MS 24 communicate on a signaling plane. The MS 20, MS 24, MG 14, and MS 16 communicate on a user plane.
An Initial Address Message (IAM) message is sent in 30 from CCN 10 to CCN 12 providing call setup information. Next, in 32, the CCN 12 selects the MG 16 and seizes MG resources for the connection end point. An identifier for MG 16 is sent back from CCN 12 to CCN 10 at 34 (e.g., APM (Bearer Control Unit Identifier (BCU-ID)). At 36, the CCN 10 then selects a MG and seizes MG resources for the connection end point. Triggered from CCN 10, MG 14 starts bearer establishment procedures at 38. When Internet Protocol (IP) is used as the user plane transport protocol and BICC is used as the call control protocol, then bearer setup messages are tunneled (not shown) via call control nodes, CCN 10 and CCN 12.
In practice, oftentimes the succeeding node CCN 12 can select from a set of MGs without knowing which MGs can be selected in the preceding node CCN 10. Consequently, there is no guarantee that the MG selected in CCN 12 can also be selected in CCN 10. If CCN 10 and CCN 12 do not select a common MG, longer user plane routes may result.
FIG. 2 is a simplified block diagram of an exemplary existing forward bearer setup utilizing three sites. A network 100 includes a preceding CCN 110 and a succeeding CCN 112. The network includes a MG 114, MG 116, and MG 118. The network includes a MS 122 in a GERAN 124. In addition, FIG. 2 illustrates a Public Switched Telephone Network (PSTN) 126. The CCN 110 and MG 114 are located in site 1. The CCN 12 is located in site 2. The MG 116 is located in site 3 and the MG 118 is located in site 4. The MS 122 and CCN 110, CCN 110 and CCN 112, CCN 110 AND MG 114, CCN 112 and MG 116, CCN 112 and MG 118, and CCN 112 and the PSTN 126 communicate on a signaling plane. The MS 122 communicates with the MG 114, the MG 116 and MG 118, the MG 118 and the PSTN 126, and the MG 114 and the MG 116 communicate on a user plane.
In this example, it is assumed that the CCN 112 has to play an announcement, for example due to Intelligent network (IN) interworking, before the call can be routed to the destination network (e.g., PSTN 126). At the end of the call setup, the MGs on three sides are involved in the call. In 130, a set message is sent from the MS 122 to the CCN 110. Next, in 132, the CCN 110 sends a BICC IAM message to the CCN 112. In 134, the CCN 112 determines that an announcement must be played (e.g., due to IN interworking). Next, in 136, the CCN 112 selects a MG to establish the bearer (user plane) and to play an announcement. As illustrated, CCN 112 selects the MG 116. In 138, the CCN 112 sends an identifier of the MG 116 backwards to the CCN 110. In this example, it is assumed that the CCN 110 is unable to select MG 116. Therefore, in 140, the CCN 110 selects another MG, in this case, MG 114. In 142, a bearer is established between the MG 114 and the MG 116 and CCN 110 establishes as well the connection between MS 122 and MG 114 (not shown). In 144, the CCN 112 continues call setup after the announcement is played. The CCN 112 identifies the call to be routed to the PSTN. Next, in 146, the CCN 112 selects a MG that can connect the user plane to the PSTN, in this case, the MG 118. Another bearer is then established between MG 116 and MG 118 at 148 and between MG 118 and PSTN 126.
Existing forward bearer setups suffer from the disadvantage of oftentimes utilizing unnecessarily long user plane routes. In addition, extra network resources are utilized for the bearer setup. It would be advantageous to have a bearer setup which conserves network resources while providing a forward bearer setup.